This invention relates to magnetic data read heads and, particularly, to a thin film magnetic read head having a magnetoresistive read transducer.
A magnetic data storage system includes, generally, a storage medium, such as a tape or desk in which the data are stored in the form of small magnetized areas; a write element, which writes data to the storage medium by magnetizing the small data bits in the medium; and a read element, which senses the recorded magnetized areas. Modern read sensors are based on the phenomenon of magnetoresistance, that is, the change in resistance of a material when a magnetic field is applied.
Magnetoresistive (MR) sensors having a spin valve structure have been employed as read transducers in magnetic disk read/write heads. Spin valve MR sensors are capable of exhibiting a giant magnetoresistance (GMR) effect, and can provide for high magnetic field sensitivity in magnetic read heads. Generally, the spin valve MR sensor includes two magnetic layers separated by a non-magnetic spacer layer. One of the magnetic layers has its magnetization direction pinned, for example by coupling to an adjacent anti-ferromagnetic (AFM) layer; the other magnetic layer is free to switch magnet position direction in the presence of an applied magnetic field. Spin-dependent electron scattering causes changes in the magnetoresistance, depending upon the angular difference between the magnetization directions in the pinned and the free magnetic layers. A low-resistance state results when the magnetic layers are ferromagnetically aligned, and a high-resistance state results in the antiferromagnetic configuration.
Various materials have been employed in the construction of the various layers of spin valve MR sensors, and some of the layers may be multi-laminate; and other layers may be present in a spin valve MR structure. A hard bias layer laterally adjacent to the spin valve structure on both sides can help stabilize the free layer. A pair of conducting leads can be formed over the hard bias layer, one on each side of the spin valve structure, to pass the sense current.
Features of a conventional spin valve MR sensor are shown by way of example in FIG. 1A. Generally, the spin valve structure 20 is formed by deposition of constituent layers of the structure over a gap layer 21, followed by masking and ion milling to remove the layers adjacent the spin valve structure 20 on either side, and to remove a surface portion of the gap layer 21 (“overmilling”). The resulting spin valve structure has sloping sides. In the bottom synthetic spin valve structure shown in this example, the layers include an antiferromagnetic (AFM) layer 22, a pinned layer 23, a free layer 24, and a capping layer 25. An underlayer 41 is formed upon the overmilled portion of the gap layer 21, and on the sloping sides of the spin valve structure 20, and a hard bias layer 44 is formed upon the underlayer 41. The hard bias layer 44 in a conventional spin valve MR sensor such as that illustrated in FIG. 1A may consist of CoPt, for example, and the underlayer 41 may consist of Cr, for example. The gap layer is typically formed of alumina (Al2O3), for example, and, where the substrate is a material different from the gap layer (for example, a silicon wafer), the gap layer is formed by deposition onto the substrate. Electrically conductive leads 46 are formed over the hard bias layer.
As is well known, the spin valve structure 20 may include other layers, and certain of the identified layers may themselves be laminates. A spin valve structure is conventionally termed a “bottom” spin valve where, as in this example, the AFM is situated below the free layer, that is, between the gap and the free layer.
The relative positions (elevations above the gap layer) of the free layer 24 and the hard bias layer 44 in the conventional spin valve MR sensor of FIG. 1A is illustrated diagrammatically in FIG. 1B. The thickness of the hard bias layer is much less than that of the spin valve structure, and appropriate alignment of the hard bias layer and the free layer is difficult to obtain using conventional processing methods. As the diagram shows, a plane generally parallel to the various layers, and located midway through the thickness 44′ of the hard bias layer, passes entirely below the free layer 24. And, as the diagram shows, a plane generally parallel to the various layers, and located midway through the thickness 24′ of the free layer passes well above the mid-plane of the hard bias layer, and in this illustration passes above the upper surface of the hard bias layer 44 in a region away from spin valve structure 20.